Long-acting beta 2-selective agonists have become a major form of therapy of reversible airway obstruction. Modern agents are effective by all routes of administration and can both eliminate bronchospasm as well as prevent its occurrence. Many drugs such as albuterol, terbutaline and fenoterol have similar pharmacologic profiles, and there is frequently little to choose between them. The majority of the available data indicate that aerosol therapy produces as much bronchodilation as the oral and parenteral routes with much fewer side effects.